When Syria's unrest began last year, the country's half-million Palestinians at first struggled to stay on the sidelines. But in recent months, many Palestinians started supporting the uprising.
The PFLP-GC, however, has remained loyal to Assad's regime.
The popular committees in Yarmouk Camp, which are led by the PFLP-GC and represent camp residents and Palestinian factions, said the camp was attacked by "terrorist gangs" who claim to include anti-government Palestinians.
"The mercenaries who claim to have Palestinians among them" tried to infiltrate the camp Sunday but were repulsed by the popular committees, the statement said. When the rebel attack failed, they fired mortars that killed and wounded several people, it added.
"Those who are shelling the camp are terrorists" who want to displace the Palestinians again, PFLP-GC spokesman Anwar Raja told The AP in Damascus.
Syrian authorities blame the anti-government uprising that began in March last year on a foreign conspiracy. They accuse Gulf countries Saudi Arabia and Qatar, along with the U.S, other Western countries and Turkey, of offering funding and training to the rebels, whom they describe as "terrorists."
In northern Syria, An opposition figure also said there were clashes between rival rebel groups for control of the Bab al-Salameh border crossing point with Turkey that has been in the hands of rebels since July. The opposition figure spoke on condition of anonymity because of the sensitivity of the matter.
The opposition figure said Sunday's fighting was between the Northern Storm Brigade and the Amr bin al-Aas brigade, which has a large number of Muslim hardliners.
There are dozens of opposition groups and rebel brigades fighting in Syria's civil war. Rivalries are common though violent clashes are unusual.